Week 8 Book Notes 20-22
Week 8 Book Notes 20-22 Chem 141
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This 8 page Class Notes was uploaded by Cassidy Zirko on Sunday October 25, 2015. The Class Notes belongs to Chem 141 at University of Montana taught by Mark Cracolice (P) in Fall 2015. Since its upload, it has received 22 views. For similar materials see College Chemistry 1 in Chemistry at University of Montana.
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Date Created: 10/25/15
Week 8 Prof Cracolice Chem 141 Chapter 20 How is Energy Related Systems and Chemical Change 101915 201 What is Energy Energy ability to do work or transfer heat Work w done to move an object is the product of Force F and the distances it is move of a certain distance d wde move distance I more work Joule J unit of work Heat a form in which energy is transferred between substances with different temperatures Higher temperature I loss of energy Temperature a measure of average energy of particles in a substance Absolute temperature is directly proportional to average kinetic energy of molecules What types of Energy are Affected by a Chemical Change 0 Exothermic reaction chemical change that releases energy to its surroundings 0 Ex Mg Se I MgSe energy 0 Endothermic Change chemical change that absorbs energy from its surroundings O 2H20 energy I 2H2 02 0 Potential Energy depends on its position in a field where forces of attraction andor repulsion are present 0 Always electrostatic forces between charged particles 0 Oppositely charged particles have a greater potential energy when they are father apart 0 Closer particles lower potential energy in a system 0 Potential energy is greater when you are close 0 Minimization of energy is one driving force that causes chemical reactions to occur 0 Kinetic energy any moving object mechanical energy What Units are Commonly Used to Express Quantity of Energy 0 Measured in Joules 1 cal 4184 4184Jcal O cal amount of energy required to raise the temperature of one gram of water up 1 C 0 both joules and calories are very small units more community used is kilojoules kJ and kilocalorie kcal O 1 kcal 4184 4184kJkcal Week 8 Prof Cracolice Chem 141 0 British Thermal Unit BTU amount of heat required to raise the temperature F of one pound of water by 1 0 How do Food Calories Relate to Other Energy Units Calorie Cal used by nutritionists to measure food energy 0 l Calorie Food 1000 cal 0 Always written with a capital C 0 Wide range of caloric intake per person 0 202 How is Energy Stored In and Moved In and Out of a Chemical System I What is a Thermodynamic System 0 Thermodynamic System the portion of the universe under consideration 0 Classified as either open or closed 0 Open system has imaginary boundary matter can move in and out of the system I Ex Lake I oxygen going in and out as well as other organisms 0 Closed system has physical barriers that keep quantity of matter in the system constant I Ex lab experimental systems 0 The term surrounding is used to escribe everything outside of the thermodynamic systems 0 How do Properties Depend on the History of the System 0 State function property whose volumes determine only by the state of a system at a given moment 0 Doesn t depend on the history of the system I Ex distance from San Francisco to Denver I not state function I Change in elevation is a state function because it is independent of path 0 How is Energy Stored in a Chemical System 0 External energy is not a valid concept I Ex external energy baseball ying through the air potential energy based on height above earth kinetic energy mass and speed of ball External because it depends on something outside of the ball Molecules all have their own potential and kinetic energy 0 Internal energy energy of a system that results from sources other than the OO in uence of external forces Precise value of internal energy is unknown except for the simplest systems 0 Change of internal energy of a system to be calculated without knowing its actual 0 value 0 How is Energy Moved in and Out of a Chemical System 0 Laws of thermodynamics 0 Law of Conservation of Energy energy can neither be created nor destroyed 0 Energy added to or removed from a system total system energy must be equal to the orginal system plus or minus the energy change Week 8 Prof Cracolice Chem 141 0 Difference in energy is equal to amount added or removed E energy of a system state function I only depends on initial energy and final 0 states of the system 0 Second Law of Thermodynamics Heat ows into or out of a system internal energy of the system changes by a quantity equal to the quantity of heat transferred 0 work can be done on a system that adds internal energy to the system 0 work helps us understand the first law of thermodynamics First Law of Thermodynamics internal energy of a system changes by an amount equal to the sum of the heat that ows into or out of the system and work AEqw AE A 0 When system gains heat q is positive system loses heat q 0 Energy added w work done by system energy lost I w 203 What Thermodynamic Quantity is Used to Expressed the Heat Content of a System 0 Heat ow q is not a state function 0 Some conditions where heat absorbed or produced by a system depends only on the initial and final states of the system 0 Eintended energy P pressure Vvolume Enthalpy H HE AEPA V 0 Pressure volume of work I work associated with chemical change in a liquid and a gas phase w PAV 0 Negative because external force causes change in a volume of system 0 Work due on a system positive work AEzq PAV I AHq PAV PAV AHqu 0 Constant pressure p relationship restricted to constant and pressure process 0 Enthalpy is a state function 0 Only need to know initial and final sates of the system Week 8 Prof Cracolice Chem 141 AH Heat of Reaction Enthalpy of Reaction when a system gives off heat to surroundings exothermic change enthalpy of a system goes down and A H has a negative value d A H When reaction absorbs heat endothermic changer enthalpy increases an is positive 204 How Does Energy Change Relate to Amounts of Species in a Chemical Change Thermochemical equation equation that includes a change in energy One type involves A H for reaction to right of the conventional equation 0 EX 2C2H6g 7 02g D 4C02g 6H20g A H 2855kJ Second includes energy as a reactant or a product 0 EX 2C2H6g 7 02g I 4C02g 6H20g 2855kJ AH Endothermic reaction heat is reactant or positive value Have to use state symbols because size of enthalpy changes depending on state of reactants and products Assume that water is a liquid unless otherwise stated Relationships of energy is similar to relationship of moles coefficients Amount of energy can be used in a proportional stoichiometry problem Chapter 21 What are the Relationships among Heat Energy Temperature and Mass for Pure Substances Book Notes 102115 211 What are the Relationships among Heat Energy Temperature and Mass for Pure Substances Change from a liquid to a solid I heat is removed Liquid to a gas I heat is added How does Heat Energy Change With a Change of State of a Pure Substance O A Hvap enthalpy of vaporization q 0c m I A Hvap m q I We AHWP AHWP 0 Units energy per quantity ex kJg Week 8 Prof Cracolice Chem 141 AHW 0 At the particulate level p I energy needed to overcome the attractive forces among the particles of a liquid I energy of particles becomes so high that it overpowers the attraction O Enthalpy 0139 Heat of Condensation the energy required to condense a liquid into a gas at its boiling point AHW 0 Heat is removed from the substance Exothermic change 0 Most common problem to solve I finding energy added or removed in a change of state using the equation q 2 m A Hvap Mm A Hmp 0 Usually a smaller number than 0 Heat of solidification going from liquid to solid is numerically Mm o qmAHfus 0 Remember that q is heat ow 0 How does Heat Energy Change With a Change in Temperature of a Pure Substance ATzT nal T I ATsz Tl initial 0 AT AT O C m A T Where c is the constant that change the proportionality q 0c m AT to an equation c specific heat expressed in Jg Z 0C or JgK Specific Heat c heat ow required to change the temperature of one gram of a substance by one degree centigrade Low specific heat I gains energy When heating High specific heat best at retaining energy At 4184 Jg Z 0C wat has one of the highest specific heat 0 In problems you will always be given at 3 of the 4 components of q mc A T AT D Q mmass cspecific heat of substance change in temperature Week 8 Prof Cracolice Chem 141 I What if there is a Change in Temperature and a Change in State 0 I ice I water vapor through heating steadily O O Find heat ow at step four with I First step ice would warm to melting point I Second step ice would melt at melting point I Third step water would warm to boiling point I Fourth step water would boil at boiling point I Fifth step steam would continue to become hotter Specific heat is used to calculate heat ow for steps 135 using 9 2 m0 A T Find heat ow at step two with A Hfus using q 2 A Hfusm AHW p using qZAHvapm Total heat ow is the sum of all of the individual q from eat step Chapter 22 How are Heat Energy Change Determined 102315 221 What Experimental Methods are Used to Determine Heat Transfer 0 Law of Conservation of energy energy can neither be created nor destroyed I All heat energy released by a substance must be gained by another I How is Heat Transfer Determined at Low Cost 0 O 0 000 Very Common to have to find the specific heat of a metal or the heat of a reaction Cheapest way done in a Styrofoam cup because it holds the heat very well Calorimetry where heat transfer is used to determine specific heat or the heat of a reaction Calorimeter isolated segment of the universe that can neither transfer heat from nor to the surroundings An experiment of this type is never perfect Measurements of imperfections are included in all experiments Sum of heat transfer must be zero I qX qy qcal 0 where x and y are parts of the reaction In a perfect experiment qcal would be zero You can use q mCA T Some heat transfer to calorimeter so there is a calorimeter constant Week 8 Prof Cracolice Chem 141 O O O O Calorimeter constant Kcal heat ow per unit of change in temperature q KcalE I qKcalAT First step is to determine the value of Kcal Dilute acid and base solution have the same density and specific heat as water 0 How is Heat Transfer Determined in Research Labs 0 Bomb Calorimeter or Combustion Calorimeter most common device used in labs to measure the heat of a reaction using a metal bom Where the reaction takes place AH At a constant pressure is equal to q heat ow AH At different pressures is not equal to q Use A H q W I A H qv Where V is the constant volume AHZAEAPV lbomb calorimeter AquAPV K calorimeter and water is caICUIated qreaction qcal qH20 qreaction qBC 0 BC bomb calorimeter calorimeter and H20 can be considered as a single unit With a single calorimeter constant qrxn A T qBCZ qrxnzKBCAT I KBC Most common KBC 264kL g Which is solid benzoic acid Commonly used in bomb calorimeters 222 How Does the Heat Content of a System Change as a Result of a Chemical Change 0 A H final amount of heat minus initial amount of heat OR heat content of products minus heat content of reactants 0 How is the Heat Content of an Element or Compound determined 0 Enthalpy or heat of function A Hf change in enthalpy for the reaction in Which pure stable elements react at a pressure of 1 bar if they are a gas to form one mole of product also at 1 bar if it is a gas Basically the heat of the reaction based on the heat of a series of chemical equations to form the final complete chemical equation 0 represents standard conditions only one mole of products is formed at one bar of pressure and pure and stable elemental reactant at 1 bar f represents formation enthalpy specifies the type of heat in the reaction formation from the formation of a compound A H Elements in standard states have f of zero You need to know the states of common elements Week 8 Prof Cracolice Chem 141 0 Liquids bromine and mercury o Gases hydrogen nitrogen oxygen f39louring chlorine and all 8A18 elements helium neon argon krypton xeon radon 0 Diatomic elements hydrogen nitrogen oxygen uorine chlorine bromine and iodine 0 Carbon standard form I graphite or diamond have to specify 39 6X Cs graphite 0139 Cs diamond AH 0 must specify states of all species in a reaction because their f will vary depending on the state 0 can use fractional coefficients on reactants because the reactants can only make one mole of product coefficient of products is one 0 products of coefficient must be 1 0 How is the Change in Heat Content Resulting from a Chemical Change Determined n A Hf Z reactants O nAHfZ productsz A 11 2 z z 0 11 number of moles of that specific species 0 A Hf standard enthalpy of formation of species 0 To find the total change in heat content take the sum of the heat from each individual elementcompound added together of the product and subtract the sum of the heat from each of the elementscompounds added together of the reactants 223 What is the Relationship of the Change in Heat Content Between a Single Reaction Step and the Entire Reaction 0 enthalpy is a thermochemical property of every stubstance and is a state function 0 Hess s Law if a reaction is carried out in a series of steps the A H for the total reaction will be equal to the sum of A H for each step 0 Enthalpy of combustion is the A H when one mole of substance is burned with an excess of oxygen 0 You can split one chemical reaction into multiple chemical reactions and take the A H for each step of the reaction 0 However you manipulate the equation you must always manipulate your A H in the same way 0 Ex Main equation Mn02s 2CS graphite I Mns 2 COg can be broken into 0 Mns Dug I Mn02s and Csgraphite 12 02g D COltggt
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